The present invention relates to subsurface imaging using ground-penetrating radar. It relates more particularly to a method that makes it possible, starting from a fixed point, to explore subsurface geological structures and to detect obstacles buried a short depth beneath the surface (pipelines in the field of civil engineering, mines in a military application, etc.).
According to another aspect of the invention, it relates to ground-penetrating radar implementing this method of subsurface imaging from a fixed point.
For planetary missions, and for Mars in particular, such ground-penetrating radar systems in fact seem to be the most suitable instruments for subsurface exploration; in particular this is because they are well adapted to the severe constraints that these missions impose on the mass and power of the measuring instruments.
On Earth, the use of radar for the exploration of subsurface geological structures generally requires a mobile instrument for gridding the terrain, effecting numerous measurements and using inversion algorithms for finding the structure of the underlying terrain. In fact, these instruments only record the distance of the reflectors or diffusers without measuring their direction relative to the transmitter and so can only give three-dimensional images of the subsurface provided they are moved over the surface to be probed. Now, during planetary missions such as that envisaged for the planet Mars, an automatic station will be set down on the planet""s surface and the measurements will therefore be effected from a fixed point, the lander.
Radar systems on board satellites in orbit round the surface of the planet to be probed are also known, as detecting instruments. At present the main drawback of these radar systems is that they are not powerful enough, being too far from the surface, to permit detection beyond a depth of about 100 meters.
The present invention therefore aims to overcome the aforementioned drawbacks by proposing a method of subsurface imaging comprising ground-penetrating radar that permits determination of the direction of propagation of waves reflected or backscattered by subsurface inhomogeneities and therefore measurement not only of the distance of reflectors or diffusers but also of their direction relative to the transmitter without recourse to a mobile instrument; it then being possible, on the basis of the data obtained, to construct a three-dimensional image of the underground reflectors or diffusers by means of processing and analysis algorithms.
For this purpose, the method of subsurface imaging according to the invention, using ground-penetrating radar comprising means of transmitting, receiving and processing signals, is characterized in that:
signals are transmitted from a fixed point relative to the subsurface and using at least two electrical antennae;
signals reflected or backscattered by reflectors or diffusers of the said subsurface are received by means of the said electrical antennae and of three magnetic antennae;
and the said reflected or backscattered signals are processed with the aid of an algorithm in order to obtain the said imaging of the said subsurface.